As the world strives to meet the demand for electricity, sustainable energy technologies are attracting significant attention. The world has set its sights on renewable energy sources as a way to meet this demand and, at the same time, lower the world's dependence on fossil fuels and decrease carbon dioxide emissions. Currently, however, renewable energy sources such as solar energy, wind power, hydropower, biofuel, biomass, and geothermal energy only supply a small amount of the electricity consumed worldwide. Little electricity is currently produced from renewable energy sources because of the relatively high cost associated with the materials and the technology used to generate electricity from these renewable energy sources. This is especially true for solar electricity generation.
The two most common forms of solar electricity generation are solar thermal generation and solar photovoltaic generation. Solar thermal generation converts solar energy into heat and then uses the heat to generate electricity. A typical solar thermal generation process consists of storing the heat from solar energy in a fluid and then using the heated fluid in mechanical engines such as Stirling engines or Rankine engines to generate electricity. Solar photovoltaic generation converts solar energy directly into electricity. While the cost [$/W] of the solar thermal electricity generation is lower than the cost of solar photovoltaic electricity generation, solar thermal electricity generation is mostly effective for large size systems and is not readily scalable for distributed power generation in residential homes or office buildings. On the other hand, solar photovoltaic generation is scalable and is widely used in residential locations; however, photovoltaic cells are expensive and the solar energy that is not used by the photovoltaic cell is wasted in the form of heat.
An alternative to solar thermal electricity generation and solar photovoltaic electricity generation is the direct conversion of solar energy into electricity by a solar thermoelectric system. Thermoelectric generators convert thermal energy directly into electricity, relying on the Seebeck effect in solid materials. The Seebeck effect is a process whereby a temperature difference across a material generates electricity. In a solar thermoelectric generator, solar radiation is absorbed and the heat generated from the solar radiation is transferred to the hot side of the thermoelectric device, thereby creating a temperature difference across the thermoelectric device which produces electricity via the Seebeck effect. Also, solar thermoelectric generators are scalable and relatively cost effective for residential applications.
Regardless of what solar electricity generation system is used, the main problem associated with solar energy is that it is an inherently intermittent energy source. Solar radiation output varies throughout the day and is often affected by cloud cover. Thus, an important aspect of solar electricity generation is being able to store solar energy and being able to use the solar energy to generate electricity to meet the demand when the solar radiation output is low. Another problem with solar electricity generation is that the conversion efficiency between solar energy to electricity is low and a substantial amount of solar energy is wasted in the form of heat. To counteract this, the wasted heat from the solar electricity generation could be recovered and used for a solar fluid heating system or for another thermoelectric generation system and therefore increase energy conversion efficiency.